Rechargeable Aqueous Zn-ion Batteries Research Articles

Regulation of Zn2+ Solvation Configuration in Aqueous Batteries via Selenium-Substituted Crown Ether Engineering.

The efficient utilization of the metallic Zn in rechargeable aqueous Zn-ion batteries (RAZBs) struggle to suffer from parasitic Zn dendrite formation, hydrogen evolution reactions as well as severe interfacial degradation at high areal capacity loadings. This study thus proposes to employ the modified crown ether as an aqueous electrolyte additive to regulate the Zn2+ desolvation kinetic and facilitates the horizontally oriented (002) deposition of Zn, extending the lifespan of both the symmetric cell and full cell models. Specifically, zincophilic cyano and hydrophobic selenium atoms are incorporated into the crown ether supramolecule to enhance Zn2+ coordination and desolvation capability. The addition of 4-cyanobenzo-21-crown-7-selenium at a low concentration of 0.5 wt.% effectively mitigates hydrogen evolution and Zn corrosion caused by water, promoting the oriented deposition of Zn2+. The Zn||V2O5 full cell prototype, assembled with the areal capacity loadings of 2 mAh cm-2 and N/P ratio of 2.95, exhibits negligible capacity fading at 2.0A g-1 for 300 cycles, highlighting the commercial feasibility of supramolecular macrocycles additive for practical RAZBs applications.

A Protective Layer of UIO-66/Reduced Graphene Oxide to Stabilize Zinc-Metal Anodes toward High-Performance Aqueous Zinc-Ion Batteries.

Rechargeable aqueous Zn-ion batteries with a Zn anode hold great promise as promising candidates for advanced energy storage systems. The construction of protective layer coatings on Zn anode is an effective way to suppress the growth of Zn dendrites and water-induced side reactions. Herein, we reported a series of UIO-66 materials with different concentrations of reduced graphene oxide (rG) coated onto the surface of Zn foil (Zn@UIO-66/rGx; x = 0.05, 0.1, and 0.2). Benefiting from the synergistic effect of UIO-66 and rG, symmetric cells with Zn@UIO-66/rGx (x = 0.1) electrodes exhibit excellent reversibility (e.g., long cycling life over 1100 h at 1 mA cm-2/1 mAh cm-2) and superior rate capability (e.g., over 1100 and 400 h at 5 mA cm-2/2.5 mAh cm-2 and 10 mA cm-2/5 mAh cm-2, respectively). When the Zn@UIO-66/rG0.1 anode was paired with the NaV3O8·1.5H2O (NVO) cathode, the Zn@UIO-66/rG0.1||NVO cell also delivered a high reversible capacity of 189.9 mAh g-1 with an initial capacity retention of 61.3% after 500 cycles at 1 A g-1, compared to the bare Zn||NVO cell with only 92 cycles.

Zn-ion ultrafluidity via bioinspired ion channel for ultralong lifespan Zn-ion battery.

Rechargeable aqueous Zn-ion batteries have been deemed a promising energy storage device. However, the dendrite growth and side reactions have hindered their practical application. Herein, inspired by the ultrafluidic and K+ ion-sieving flux through enzyme-gated potassium channels (KcsA) in biological plasma membranes, a metal-organic-framework (MOF-5) grafted with -ClO4 groups (MOF-ClO4) as functional enzymes is fabricated to mimic the ultrafluidic lipid-bilayer structure for gating Zn2+ 'on' and anions 'off' states. The MOF-ClO4 achieved perfect Zn2+/SO4 2- selectivity (∼10), enhanced Zn2+ transfer number ([Formula: see text]) and the ultrafluidic Zn2+ flux (1.9×10-3 vs. 1.67mmol m-2 s-1 for KcsA). The symmetric cells based on MOF-ClO4 achieve a lifespan of over 5400h at 10mAcm-2/20mAhcm-2. Specifically, the performance of the PMCl-Zn//V2O5 pouch cell keeps 81% capacity after 2000 cycles at 1Ag-1. The regulated ion transport, by learning from a biological plasma membrane, opens a new avenue towards ultralong lifespan aqueous batteries.

Achieving Highly Stable Zn Metal Anodes at Low Temperature via Regulating Electrolyte Solvation Structure.

Zinc metal is an attractive anode material for rechargeable aqueous Zn-ion batteries (ZIBs). However, the dendrite growth, water-induced parasitic reactions, and freezing problem of aqueous electrolyte at low temperatures are the major roadblocks that hinder the widely commercialization of ZIBs. Herein, tetrahydrofuran (THF) is proposed as the electrolyte additive to improve the reversibility and stability of Zn anode. Theoretical calculation and experimental results reveal that the introduction of THF into the aqueous electrolyte can optimize the solvation structure which can effectively alleviate the H2O-induced side reactions and protect the Zn anode from corrosion. Moreover, THF can act as a hydrogen bond acceptor to interact with H2O, which can greatly reduce the activity of free H2O in electrolytes and improve the low-temperature electrochemical performance of Zn anode. As a result, the Zn anodes demonstrate high cyclic stability for 2800h at 27°C and over 4000h at -10°C at 1.0mA cm-2 /1.0mAhcm-2. The full cell exhibits excellent cyclic stability and rate capability at 27 and -10°C. This work is expected to provide a new approach to regulate the aqueous electrolyte and Zn anode interface chemistry for highly stable and reversible Zn anodes.

Regulating ionic transport and interface chemistry via high-dielectric BaTiO3 porous scaffolds for aqueous Zn-ion batteries

Rechargeable aqueous Zn-ion batteries (AZIBs) are gaining considerable attention as alternatives to Li-ion batteries owing to their excellent safety, high energy density, low cost, and environmental friendliness. However, their Zn anodes suffer from severe dendritic growth, the hydrogen evolution reaction (HER), and corrosion, which limit the commercialization of AZIBs. To address this challenge, we designed a solution involving the development of a high-dielectric hydrophobic BaTiO3 (BTO) porous scaffold layer that is strategically applied to the Zn surface. This BTO layer effectively impedes the dendritic growth of Zn. The distinct polarizability of the BTO layer actively diminishes the electric-field gradient, thereby minimizing the interaction between the H2O molecules and the Zn surface. This phenomenon helps suppress dendritic growth, thus ensuring the uniform deposition of Zn and preventing the HER. The electrochemical performance of a symmetric cell containing the Zn@BTO electrode exhibits low-voltage polarization and stable charge–discharge performance for up to 500 h. In addition, a full-cell AZIB containing a high-capacity α-MnO2 cathode and Zn@BTO anode exhibits good rate capability and a long life of up to 500 cycles. This study demonstrates the development of a cost-effective dendrite-free Zn anode integrated with a highly dielectric hydrophobic BTO porous scaffold layer as a stable Zn–electrolyte interface layer for high-performance AZIBs.

Nutrient for Inhibiting the Activity of H2O and Optimizing Interfacial Chemistry for Aqueous Rechargeable Zn-Ion Batteries

Nutrient for Inhibiting the Activity of H₂O and Optimizing Interfacial Chemistry for Aqueous Rechargeable Zn-Ion Batteries

Dendrite-free zinc deposition enabled by MXene/nylon scaffold and polydopamine solid-electrolyte interphase for flexible zinc-ion batteries

The rapid growth of wearable and portable electronic devices calls for energy storage devices with good flexibility, high energy density, and safety. Rechargeable aqueous Zn ion batteries (ZIBs) with the merits of environmental benignity, high safety, and low cost have arisen as promising energy storage candidates for wearable electronic systems. However, the unstable Zn anode interface and notorious Zn dendrite formation hinder the application of flexible ZIBs. Herein, a highly stable and flexible Zn anode is developed by taking advantage of highly conductive Ti3C2 MXene coated nylon fabric (MXNY) as a three-dimensional (3D) Zn deposition skeleton and polydopamine (PDA) as a solid electrolyte interface (SEI). The combination of MXNY and PDA SEI provides synergistic benefits such as a stabilized interface for homogenous and dendrite-free Zn deposition and improved corrosion resistance. As a result, a flexible and stable Zn anode with improved Coulombic efficiency of 99.6 % at a current density of 10 mA cm–2 for 1 mA h cm–2, and long cycling stability of more than 3000 h at a current density of 0.5 mA cm–2 for 0.5 mA h cm–2 can be achieved. When paired with a flexible cathode, the quasi-solid-state ZIB can power various electronic devices under different mechanical deformations, indicating its promising potential as flexible energy storage devices for wearable and portable electronics.

Aqueous Zn-Tetrazine Batteries with Cooperative Zn2+/H+ Insertion.

We present the investigation of 1,2,4,5-tetrazine derivatives as low-cost and synthetically modular organic electrode materials in rechargeable aqueous Zn-ion batteries (AZIBs). The substituents at the 3,6-positions of tetrazine were found to be critical for cycling stability. While heteroatom substituents (chloro, methoxy, and pyrazole) lead to the rapid decomposition of electrode materials in the electrolyte, the installation of phenyl groups enhances the cycling stability via π-π stacking. Spectroscopic characterization suggests a cooperative Zn2+ and H+ insertion mechanism. This unique cooperativity of Zn2+ and H+ leads to a steady discharge plateau in contrast to the undesirable sloping voltage profile typically observed in Zn-organic batteries.

Galvanic stabilization of Zn metals for long-life aqueous batteries

Rechargeable aqueous Zn-ion batteries have received extensive attention due to their environmental friendliness, high safety, and low cost. However, the Zn dendrite growth during plating/stripping cycles, which deteriorates coulombic efficiency and shortens the cycle life, dramatically hinders the application of Zn anodes in batteries. Herein, we propose to grow an In layer on Zn foils through spontaneous Galvanic reaction to address the challenging Zn dendrites. In-situ optical observations show that this strategy effectively suppresses the dendrite growth, thereby leading to a robust and stable Zn metal anode with low voltage hysteresis (30 mV at 0.4 mA·cm−2) and long cycle life of over 1200 h in symmetric cells. Meanwhile, the full cell assembled with the modified Zn anode and MnO2 cathode exhibits excellent cycling performance over 2000 cycles and a high discharge capacity of 89.1 mAh·g−1. This work provides an efficient pathway for interfacial engineering towards stable Zn anodes.

A High‐Capacity and High‐Voltage Aqueous Zn‐Polymer Battery with Self‐Charging Function

AbstractOrganic electrodes in aqueous batteries rely on electrochemical redox reactions for charge and discharge. The organic cathode at a discharged state can be spontaneously oxidized when exposed to air, which facilitates the development of air‐charging batteries. However, polymer cathodes in aqueous rechargeable Zn‐ion batteries (ARZIBs) generally show low discharge median voltage below 1 V. Herein, a new polymer cathode is reported that is prepared by electrodepositing poly(4‐hydroxydiphenylamine, HDPA) onto mesoporous activated carbon and shows a relatively high discharge voltage plateau at ≈1.1 V when coupled with a Zn anode. Its self‐charging performances at different conditions are investigated. Also, a high areal capacity of 3.8 mAh cm−2 of the cathode is achieved. The poly(4‐HDPA) contains both amino and carbonyl groups, and the carbonyl group is found to be fully responsible for redox reaction. Further investigation suggests that both Zn2+ and H+ in the ZnSO4 electrolyte participate in the charge storage process, and the H+ plays a dominant role. The air‐charging mechanism of this polymer cathode is elucidated both experimentally and theoretically. To demonstrate the practical applications, prototypes of box‐shaped battery pack are air‐charged to either drive a mini electric fan or light up LEDs.

Clarifying the Limitations of Copper Hexacyanoferrate in Rechargeable Aqueous Zinc-Ion Batteries Via in Situ X-Ray Techniques

Copper hexacyanoferrate (CuHCF) is a compound belonging to the Prussian Blue Analogue (PBA) family, known for its open structure with cubic symmetry and large cavities capable of accommodating various cations, such as alkali-metal ions and divalent cations, making it an interesting candidate for ion-insertion batteries.CuHCF has been increasingly attracting attention for innovative approaches in rechargeable aqueous batteries which represent an emerging alternative technology for realizing sustainable and efficient stationary storage of intermittent electricity produced via renewable sources1.CuHCF stands out as an environmentally friendly cathode material in rechargeable aqueous Zn-ion batteries (ZIBs), enabling the realization of cost-effective and safe cells that support elevated charge/discharge rates and thus provide high power delivery2, 3. Relying only on abundant, inexpensive and non-toxic materials, combined with non-flammable and mildly acidic electrolytes, Zn/CuHCF cells are an attractive electrochemical system for addressing the challenges of developing energy storage devices for power grids due to their quick response and contained fabrication costs, although their energy density is intrinsically limited4 (< 100 Wh·kg-1).CuHCF displays one of the highest operating potentials (≈1.7 V vs. Zn2+/Zn) among cathode materials in aqueous ZIBs2, 3 and a modest capacity of ≈60 mAhg-1. Yet, what sets CuHCF apart is its ability to undergo ion insertion/de-insertion with negligible structural variations or volume changes5, making these electrodes apt for extensive cycling under heavy-duty conditions without risking induced mechanical or electrical damages causing early cell failure.However, a series of obstacles are present along the way of Zn/CuHCF cell development. Aside from issues on the Zinc side (e.g. uncontrolled Zn deposition/stripping), notoriously challenging in terms of interface stabilization6 and effective utilization4, significant limitations arise from the CuHCF ageing mechanisms during cycling. Such mechanisms have remained elusive so far, mostly due to the complexity of this compound and a simultaneous interaction of various species in the electrochemical processes. To date, there have been only speculative attempts to explain the capacity fading in CuHCF and, consequently, only a few scenarios have been suggested for it. Possible phase segregation and formation of spurious, non-stoichiometric Zn-rich phases (e.g. ZnxCu1-xHCF) have been argued7-9, while also signs of Cu dissolution were previously detected10, yet thought to be minimal and not affecting the CuHCF performances.Here, we will shed light on the limitations of CuHCF during cycling in ZIBs and explore its ageing mechanism by conducting a thorough study employing X-ray techniques11. Our investigation reveals that CuHCF is less stable than previously assumed, and that its debated Cu dissolution is linked to the ageing process11, forming Cu vacancies that can accept Zn2+. This Cu dissolution also results in a gradual activation of the Fe3+/Fe2+ couple, which has unambiguously been assigned to the appearance of a plateau on charge at ≈1.8 V vs. Zn2+/Zn (Figure 1). This is believed as the main contributor to the subsequent capacity loss. These insights into the CuHCF ageing in ZIBs may help in devising strategies to mitigate this critical aspect and improve battery performances in terms of stability and cycle life. Figure 1. (a) Scheme of an aqueous Zn/CuHCF cell. (b) Galvanostatic charge-discharge profiles of a Zn/CuHCF cell between 1.00 and 2.15 V at 0.6 mAcm-2. Note the emergence of a sloping plateau around 1.8 V and a slight capacity loss after 200 cycles. Acknowledgements M.V. acknowledges the funding by the ÅForsk Foundation, the support by the Swedish Electromobility Centre, the Swedish Energy Agency and StandUp for Energy. References C. D. Wessells, R. A. Huggins and Y. Cui, Nature communications, 2011, 2, 1-5.R. Trócoli and F. La Mantia, ChemSusChem, 2015, 8, 481-485. Z. Jia, B. Wang and Y. Wang, Materials Chemistry and Physics, 2015, 149, 601-606.G. Zampardi and F. La Mantia, Nature communications, 2022, 13, 687. V. Renman, D. O. Ojwang, M. Valvo, C. P. Gómez, T. Gustafsson and G. Svensson, Journal of Power Sources, 2017, 369, 146-153. Z. Cao, P. Zhuang, X. Zhang, M. Ye, J. Shen and P. M. Ajayan, Advanced Energy Materials, 2020, 10, 2001599.G. Kasiri, R. Trócoli, A. B. Hashemi and F. La Mantia, Electrochimica Acta, 2016, 222, 74-83. R. Trócoli, G. Kasiri and F. La Mantia, Journal of Power Sources, 2018, 400, 167-171. G. Kasiri, J. Glenneberg, A. B. Hashemi, R. Kun and F. La Mantia, Energy Storage Materials, 2019, 19, 360-369. J. Lim, G. Kasiri, R. Sahu, K. Schweinar, K. Hengge, D. Raabe, F. La Mantia and C. Scheu, Chemistry–A European Journal, 2020, 26, 4917-4922. M. Görlin, D. O. Ojwang, M.-T. Lee, V. Renman, C.-W. Tai and M. Valvo, ACS Applied Materials & Interfaces, 2021, 13, 59962-59974. Figure 1

Rare earth metals ion intercalated hydrated vanadium oxides for high-performance aqueous zinc-ion batteries

Hydrated vanadium oxide (V2O5·nH2O) is promising cathode candidates for aqueous rechargeable Zn-ion batteries (ZIBs) owing to its high theoretical specific capacity, abundant resources and environmentally friendly. However, the higher charge density of Zn2+ lead to its structural instability, cyclic degradation and sluggish Zn2+ diffusion kinetics. Herein, rare earth metal ions intercalated into the interlayer of V2O5·nH2O materials (abbreviated as RE-VOH) are successfully synthesized to expand interlayer spacing and stabilize the layered structure via a simple sol-gel method, among, the yttrium ion intercalated V2O5·nH2O (Y–VOH) exhibits a honeycomb porous microstructure and a remarkably enlarged interlayer distance (13.6 Å), which can not only increase the contact area between the electrode material and the electrolyte but also offer rapid diffusion channel for Zn2+. Meanwhile, the problem of vanadium dissolution of cathode materials is inhibited by the electrolyte additive strategy through adding suitable vanadium oxide sol to aqueous electrolyte, furthermore, the zinc anode modification strategy in electroplating process inhibits the formation of zinc dendrites. Benefitting from the synergistic effect of modification design for the ZIBs systems of cathode, electrolyte and anode, the overall electrochemical performance of Y–VOH electrode is significantly improved, delivering a large specific capacity of 337 mAh g−1 at the current density of 500 mA g−1 and excellent rate capability of 170 mAh g−1 at 10 A g−1, along with an outstanding capacity retention of 90 % over 3000 cycles. Additionally, systematical ex situ characterizations prove the (de)intercalation reversibility of Zn2+ storage mechanism for the Y–VOH cathode. This research may provide a new way for exploiting high performance vanadium-based materials for aqueous ZIBs.

Decorating carbon quantum dots onto VO2 nanorods to boost electron and ion transport kinetics for high–performance zinc–ion batteries

Rechargeable aqueous Zn–ion batteries (RAZIBs) are regarded as attractive alternatives for large–scale energy storage. V–based cathode materials have gained great attention due to the merits of rich valence states, controllable morphology, diverse crystal structures, and controllable chemical compositions. However, the development of high–performance V–based cathode is still impeded by sluggish electron/ion transport kinetics. To address this issue, this work reveals that the electrochemical performance of the VO2 cathode can be significantly boosted by decorating carbon quantum dots (CQDs) onto the VO2 nanorods via a facile hydrothermal reaction. The VO2/CQDs sample is characterized to have strong interface interaction with the presence of CO bond. Compared to the CQD–free counterpart, the obtained VO2/CQDs sample exhibits higher specific surface area (18.7 vs 4.4 m2 g−1), better electrolyte wettability (53° vs 114° for contact angle), reduced charge–transfer resistance (1.8 vs 19.9 Ω), and facilitated ion diffusion coefficient (1.66 × 10−10 vs 4.56 × 10−11 cm2 s−1). Benefiting from these features, a high attainable capacity of 427 mAh g−1 at 0.2 A g−1 can be reached for VO2/CQDs, corresponding to the specific energy of 333 Wh kg−1 (based on the mass of VO2/CQDs). When the current density increases to 8 A g−1, VO2/CQDs can still deliver 309 mAh g−1, showing great promise for high–rate capability. Moreover, the VO2/CQDs cathode renders stable cycle performance with retaining 229 mAh g−1 after 2000 cycles. By contrast, the unmodified sample demonstrates moderate electrochemical performance (373 and 186 mAh g−1 at 0.2 and 8 A g−1, respectively). The results highlight the importance of the CQDs decoration strategy, which can effectively boost electron/ion transport in oxide–based cathodes for high–performance RAZIBs.

Interface engineering of heterostructured vanadium oxides for enhanced energy storage in Zinc−Ion batteries

Rechargeable aqueous Zn−ion batteries (RAZIBs) with the merits of cost effectiveness and high safety have been rejuvenated as tantalizing energy storage systems to meet the demand for grid−scale applications. Currently, the energy storage capability of the positive electrode (cathode) holds the key for the overall performance of RAZIBs. In this work, we reveal VO2, V10O24·12H2O (HVO), and VO2/HVO can be prepared via hydrothermal reaction by using different reducing agents. VO2 exhibits high capacity of 237 mAh/g at 4 A/g, while it suffers from quick capacity decay with 48 % retention after 2000 charge/discharge cycles. On the contrary, HVO demonstrates moderate capacity but meritorious cycle stability (i.e., 173 mAh/g at 4 A/g and 82 % after 2000 cycles). By integrating the merits of high−capacity VO2 and high−stability HVO, the biphasic VO2/HVO sample exhibits promising electrochemical performance with high capacity (317 and 239 mAh/g at 1 and 4 A/g, respectively) and good cycle stability (80 % after 2000 cycles). As examined by band structure analysis, the superior electrochemical performance of VO2/HVO is attributed to the presence of a heterojunction between VO2 and HVO enabling a built−in electric field to boost electron transport kinetics, leading to high attainable capacity and reliable cycle performance in RAZIBs.

In-situ grown hydrophilic-zinophilic ZnCr2O4 protective layer to guide horizontal Zn2+ deposition for dendrite -free Zn anodes for aqueous Zn-ion batteries

Aqueous rechargeable Zn-ion batteries (ARZIBs) have attracted much attention owing to their safety, high energy density and environmental friendliness. However, zinc dendrites and corrosive reactions during platting/stripping on the surface of Zn anodes limit the practical applications of ARZIBs. Herein, the hydrophilic and zinophilic ZnCr2O4 interface layer is grown in situ on the surface of Zn metal to stabilize Zn anode. The in-situ grown ZnCr2O4 interface protective layer constrains the 2D diffusion of Zn2+and homogenizes the surface electric field, guiding preferentially horizontal deposition of Zn2+ along the Zn foil surface. In addition, the in situ ZnCr2O4 interface layer possesses strong hydrophilicity and zinophilicity to enable rapid desolvation of Zn(H2O)62+ and improve Zn2+ platting/stripping kinetics for dense Zn deposition without dendrite Zn growth. Consequently, the symmetric cell with ZnCr2O4-protected Zn anode can stably operate more than 1500 h at 1 mA cm−2 with 1 mAh cm−2, while the Cu||ZCO@Zn half-cell presents a high average Coulombic efficiency of over 99.7 % during cycling for more than 100 cycles. In addition, the NH4V4O10||ZCO@Zn full cell exhibits the capacity retention of 83.3 % at 3 A g−1 after 1000 cycles. This investigation provides a feasible strategy to efficiently inhibit zinc dendrites by in-situ constructing hydrophilic-zinophilic artificial protective coating on the surface of Zn anodes.

Interfacial Modification of a Zn Anode by Amorphous Se toward Long-Life and Hydrogen Evolution-Free Aqueous Rechargeable Batteries.

The Zn anode in rechargeable aqueous Zn-ion batteries suffers from hydrogen gas evolution and dendrite growth, which are critical issues that make the battery impractical. Here, the Zn anode performance is greatly improved by coating an amorphous selenium overlayer with a simple chemical bath reaction process. The reduction of SeO32- ions by the Zn metal leads to the formation of an amorphous Se layer, and the optimal reaction time that determines the thickness of the Se coating as well as the Zn anode performance is found to be 2 h. The symmetric cell using Zn@Se exhibits improved rate performance and an ultralong cycle life of 4500 h after being tested at 1 mA cm-2 and 1 mAh cm-2, respectively. Compared to the bare Zn anode, the Zn@Se anode leads to a larger Zn2+ transference number and reduced charge transfer resistance. The button-type MnO2∥Zn@Se full cell exhibits higher capacity and a much longer cycle life compared to the counterpart using a bare Zn anode. Also, pouch-type MnO2∥Zn@Se full cells with a high capacity of 9.7 mAh cm-2 are made to demonstrate the inhibition of hydrogen evolution and practical applications. It is found that the in situ formation of an amorphous ZnO nanosheet network induced by the amorphous Se overlayer plays a key role in enhancing the Zn anode performance.

Strategies for Optimizing the Zn Anode/Electrolyte Interfaces Toward Stable Zn-Based Batteries.

Aqueous rechargeable Zn-ion batteries (ARZIBs) have attracted extensive attention because of the advantages of high energy density, high safety, and low cost. However, the commercialization of ARZIBs is still challenging, mainly because of the low efficiency of Zn anodes. Several undesirable reactions (e.g., Zn dendrite and byproduct formation) always occur at the Zn anode/electrolyte interfaces, resulting in low Coulombic efficiency and rapid decay of ARZIBs. Motivated by the great interest in addressing these issues, various optimization strategies and related mechanisms have been proposed to stabilize the Zn anode-electrolyte interfaces and enlengthen the cycling lifespan of ARZIBs. Therefore, considering the rapid development of this field, updating the optimization strategies in a timely manner and understanding their protection mechanisms are highly necessary. This review provides a brief overview of the Zn anode/electrolyte interfaces from the fundamentals and challenges of Zn anode chemistry to related optimization strategies and perspectives. Specifically, these strategies are systematically summarized and classified, while several representative works are presented to illustrate the effect and corresponding mechanism in detail. Finally, future challenges and research directions for the Zn anode/electrolyte interfaces are comprehensively clarified, providing guidelines for accurate evaluation of the interfaces and further fostering the development of ARZIBs.

Shackling the aqueous electrolyte via metal-organic frameworks to realize high energy density zinc-ion batteries

Ocean-like free water in conventional aqueous electrolytes leads to narrow operating voltage and parasitic reactions in rechargeable aqueous Zn ion batteries (AZIBs), which is highly undesirable. Herein, a quasi-solid aqueous electrolyte (QSAE) with a typical bulk liquid electrolyte confined inside the sub-nanoscale channels of metal-organic framework (MOFs) is proposed to tackle this issue. Detailed experiments and theoretical calculations suggest that the unfavored side reactions, e.g., corrosion, hydrogen evolution reaction, and dendrite growth on zinc surface can be effectively depressed and the electrochemical window can be expanded to 2.51 V (based on OER), achieved by the proposed MOF-QSAE because of the tailored solvation structure of Zn2+ and the restrained activity of water molecules in MOF-QSAE. Thanks to the unexpected merits of MOF-QSAE, a fabricated Zn|MOF-QSAE|V2O5 full cell exhibits an ultra-high coulombic efficiency (average value≈99.98 %) and cycle stability (capacity retention: 81.89 % after 2000 cycles). The Zn|MOF-QSAE|V2O5 full cell can even work at a low temperature of −10 ℃ for 4000 cycles without obvious performance degradation. In addition, a high-voltage AZIBs based on zinc hexacyanoferrate (ZnHCF) cathode yields an average operating voltage of more than 1.70 V and a high energy density of ≈102 Wh kg−1, further validating the practicality of the MOF-QSAE. The proposed new type of QSAE could pave a new way for the commercialization of aqueous batteries.

Flexible and Stable N-Isopropylacrylamide/Sodium Alginate Gel Electrolytes for Aqueous Zn-MNO2 Batteries

Rechargeable aqueous Zn-ion batteries (ZIBs) have attracted considerable attention owing to their high theoretical capacity of 820 mA h g−1, low cost and intrinsic safety. However, the electrolyte leakage and the instability issues of Zn negative electrodes originating from side reactions between the aqueous electrolyte and Zn negative electrode not only restrict the battery stability, but also result in the short circuit of aqueous ZIBs. Herein, we report a flexible and stable N-isopropylacrylamide/sodium alginate (N-SA) gel electrolyte, which possesses high mechanical strength and high ionic conductivity of 2.96 × 10−2 S cm−1, and enables the Zn metal negative electrode and MnO2 positive electrode to reversibly and stably cycle. Compared to the liquid electrolyte, the N-SA hydrogel electrolyte can effectively form a uniform Zn deposition and suppress the generation of irreversible by-products. The assembled symmetric Zn/Zn cells at a current density of 1 mA cm−2 (capacity: 1 mAh cm−2) show a stable voltage profile, which maintains a low level of about 100 mV over 2600 h without an obvious short circuit or any overpotential increasing. Specially, the assembled Zn/N-SA/MnO2 batteries can deliver a high specific capacity of 182 mAh g−1 and maintain 98% capacity retention after 650 cycles at 0.5 A g−1. This work provides a simple method to fabricate high-performance SA-based hydrogel electrolytes, which illustrates their potential for flexible batteries for wearable electronics.

Influence of MXene-assisted multifunctional interface on zinc deposition toward highly reversible dendrite-free zinc anodes

The ever-growing demand for safe and renewable energy storage systems has driven the renaissance of aqueous zinc (Zn)-metal batteries (ZMBs). Zn metal has the characteristics of high specific capacity, low cost, environmental friendliness, and intrinsic safety, but severe side reactions and Zn dendrite growth lead to low Coulombic efficiency and short cycle life of Zn metal anode, which restricts the commercial development of rechargeable aqueous ZMBs. Herein, a Ti3C2Tx MXene-derived ZnF2-rich multifunctional interfacial layer is prepared. In this architecture, the as-formed ZnF2-rich layer can redistribute Zn-ion flux on the electrode/electrolyte surface and suppress side reactions. Meanwhile, the results indicate that the ZnF2 can lower the desolvation energy barrier of Zn ions and enhance the Zn-ion transfer kinetics. Accordingly, the Zn@MXene anode delivers a long cycle life over 800 h at the current density of 5.0 mA cm−2 with a capacity of 5.0 mAh cm−2. Surprisingly, the Zn@MXene anode can still achieve dendrite-free Zn deposition for more than 320 h even at the current density of 10.0 mA cm−2 with a capacity of 10.0 mAh cm−2. Additionally, the assembled Zn@MXene//VO2 full-cell exhibits better cycling stability and more excellent rate performance compared to the pristine Zn//VO2 full-cell, implying the potential of this idea to develop high-power rechargeable aqueous Zn-ion batteries.